1. Field of the Invention
The present invention relates to polyolefin waxes used as coating materials and printing ink compositions, for example, a polyolefin wax suitable for use in printing inks and a printing ink composition containing such a polyolefin wax.
The present invention also relates to ethylene polymer composition dispersions and the use thereof, more specifically, ethylene polymer composition aqueous dispersions wherein particles of ethylene polymer composition are dispersed in water, printing ink additives comprising such aqueous dispersions, printing ink additives comprising the aforesaid particles, ethylene polymer composition organic solvent dispersions in which the aforesaid particles are dispersed in a hydrocarbon solvent, and printing ink additives comprising such organic solvent dispersions.
2. Description of the Related Art
Generally, waxes are used as additives in coating materials such as printing inks for purposes such as an improvement of abrasion resistance, reduction of tackiness, prevention of blocking, and improvements of water resistance and water repellency of the printed film. Here, “wax” is used as a generic term for organic compounds that are mainly composed of aliphatic constituents and are solid at room temperature but melt to become a low-viscosity fluid when heated.
Heretofore, known examples of waxes used in printing inks, such as inks for planographic printing and offset printing, include carnauba wax, beeswax, paraffin wax, microcrystalline wax, polyethylene wax, polypropylene wax, fatty acid amides, polytetrafluoroethylenes and so on. When a wax is used in a printing ink, the abrasion resistance is improved by the effect of wax particles present on the surface of the printed film made of the printing ink. This is due to the fact that the wax particles partly protruding outward from the ink surface is crushed by external physical pressure, spreads thinly on the ink coating formed on paper or various types of film material, and protects the ink surface.
Since the wax blended into the printing ink must be blended uniformly into the printing ink, various methods are known, for example, a method in which a pulverized wax is used, a method in which a solid wax is kneaded into the ink, and a method in which a wax is dispersed in an oil or water. It should be noted, however, that with the conventional solid waxes, the surface of the printed ink in which the wax is blended has significant unevenness, which makes it impossible to obtain a clear printed image, and unless a large amount of the wax is blended into the printing ink, the desired effects cannot be obtained.
Water-based inks have been widely used in the past as inks for printing on materials such as cardboard. Since they have low abrasion resistance when they consist only of the principal constituent resin, waxes are usually added to improve the abrasion resistance. The present inventors have already proposed an aqueous dispersion of a low-molecular-weight polyolefin, which does not contain any low-molecular-weight surfactants, for such uses (see JP-A Sho 58-42207, JP-A Hei 5-156028).
Nevertheless, in recent years, as seen in offset rotary printing inks, methods in which the print matter is dried at a high temperature have become widespread. On the other hand, from the viewpoint of improving abrasion resistance, moderately soft waxes exhibit good performances, since they are easily crushed on the surface of the ink layer. In use of conventional aqueous dispersions of waxes, due to softening of the waxes, insufficient blocking resistance resulting from increased tackiness of the wax has achieved. Therefore it has been desired to realize a combination of sufficient abrasion resistance and sufficient blocking resistance even after high-temperature drying.
In oil-based printing inks, on the other hand, due to restrictions on the use of solvents related to environmental concerns, organic solvents that do not contain toluene, such as alcohols, ethyl acetate and aliphatic hydrocarbons, have been used as the dispersion solvents for waxes. However, waxes are poor solvents that are difficult to dissolve in these solvents. Therefore so-called crystallization methods, wherein the wax is once solubilized at a high-temperature and a crystallized product is obtained by cooling or by adding a poor solvent, have been difficult to apply.